Which library(ct-lib/db-lib) does the app should using for MS SQLServer?

[taozuhong]

The code is split into several pieces.

1. tds directory is the wire level stuff, it should be independent of the library using it, this will allow db-lib, ct-lib, and ODBC to sit on top.
2. db-lib directory. This is the actual db-lib code which runs on top of tds.
3. ct-lib directory. This is the ct-lib code which runs on top of tds.

I want to support Microsoft SQL Server, which library(ct-lib/db-lib) does the app should using?

[taozuhong]

The prefer library for Microsoft SQL Server is db-lib, please see the guide:
https://www.freetds.org/userguide/projects.html

TinyTDS - Simple and fast FreeTDS bindings for Ruby using DB-Library.
https://github.com/rails-sqlserver/tiny_tds

[freddy77]

Why not ODBC ?

[taozuhong]

App could connect to server via db-lib, why ODBC?

It will introduce more bugs and more layers and more complications.

[freddy77]

The problem with db-lib is that some specific features are missing (Microsoft stopped developing it many years ago). Sure, support on FreeTDS is better, you can use UTF-8 so you won't miss wide characters support but things like MARS, TVP, query notifications and others will be always missing. Potentially you can use --with-odbc-nodm option and avoid the Driver Manager layer although this remove some check DM does that you'll have to check on yourself. Obviously, if you don't need additional features and db-lib is easier for you use db-lib.